proximity sensor using a finger as the ground plate (a),
liquid-level sensing with
parallel sensor and ground (b),
and material detection and analysis (c). (Courtesy of TI)
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https://tinyurl.com/y43hlrwx--
In many applications, such as chemical storage, industrial process control, or commercial washers, it's necessary to sense the level of a liquid. In this case, the sensor and ground plates can be situated next to each other, as shown in Fig. 4b, resulting in a configuration with high sensitivity along the vertical access.
As the liquid level varies, it changes the dielectric value and hence the capacitance. This sensor configuration makes use of fringe field lines; thus, the capacitance calculations are more complicated than in the case of a simple plate.